REED: SPECIALIZATION OF PARASITIC FUNGI 381 



results: (i) conidia from Artemisia vulgaris, Lactuca muralis and 

 Lithospermum arvense infected plants of the same species but did not 

 infect each other nor some other plants tested; (2) conidia from 

 Hieracium muroriim infected H. murorum and Leontodon taraxacum, 

 the latter very slightly; (3) conidia from Senecio vulgaris infected 

 5. vulgaris and Lactuca muralis; (4) conidia from Lappa major, 

 Plantago major, Pulmonaria officinalis and Verbascum thapsiforme 

 failed to infect any host inoculated. 



Salmon (128) reports the successful infection of Plantago major 

 and P. media, using conidia from the former; negative results were 

 obtained with Plantago lanceolata, Eupatorium cannahinum and 

 Galium Aparine. 



The writer (115, 116) has carried on a very extensive series of 

 experiments with this mildew, particularly with the cucurbit hosts. 

 In the main, the mildew as found on the Hubbard squash {Cucurhita 

 maxima) was used for inoculating the various plants. It was found 

 that this mildew readily infected Cucurhita maxima (seven varieties), 

 C. moschata (three varieties), C. pepo (seventeen varieties), C. foeti- 

 dissima, Cucumis dipsaceus, C. melo (nine varieties), C. sativus (eight 

 varieties), Cyclanthera explodens, Echinocystis lohata, Lagenaria vulgaris 

 (six varieties), Momordica charantia and Sicyos angulatus. Partial 

 infection of the following was obtained: Citrullus vulgaris (seven 

 varieties), Cucumis anguria (two varieties), Ecballium elaterium, 

 Melothria scabra and Momordica balsamina. Coccinea cordifolia, 

 Luffa acutangula and L. Aegyptiaca proved to be entirely resistant. 

 To a slight extent it was possible to transfer the cucurbit mildew to 

 the sunflower {Helianthus annuus) and plantain {Plantago rugellii). 

 Efforts to transfer it to Aster cordifolius, A. laevis and Solidago caesia 

 failed. It was also found that a race of mildew occurred on Aster 

 cordifolius , A . laevis and A . sagittifolius, not passing over to Cucurhita 

 maxima nor Solidago caesia. Another race occurs on Solidago caesia, 

 infecting this species but not passing over to asters or cucurbits. 



Erysiphe graminis DC. Marchal (97) was the first to demonstrate 

 host specialization in this powdery mildew. As a result of his tests he 

 concluded that the following races may be distinguished, although he 

 gives us no details of his evidence: 



1. Tritici upon Triticum vulgar e, T. Spelta, T. polonicum and T. 



turgidum; not on T. durum, T. monococcum nor T. dicoccum. 



2. Hordei upon Hordeum hexastichon, H. vulgare, H. trifurcatum, H. 



nudum, H. juhatum and H. murinum; not on H. maritimum, 

 H. secalinum nor H. bulhosum. 



3. Secalis upon Secale cereale and S. anatolicum. 



4. Avenae upon Avena sativa, A.fatua, A. orientalis and Arrhenatherum 



elatius. 



26 



